Perceiving the sequence of speech and non-speech stimuli

The task is to estimate on which syllable of a spoken sentence a click was superimposed. Experiment I confirms Ladefoged and Broadbent's finding of a systematic tendency to prepose the click (negative displacement), but shows also that the tendency is decreased when prior knowledge of the sentence is provided. Experiment II shows that acoustic prior knowledge is not necessary to produce the decrease and that it occurs also with textual prior knowledge. Experiment III shows that the negative displacement is not eliminated by short-term practice on the task, as Fodor and Bever contended. The effect of prior knowledge is inconsistent with the explanation of negative displacement in terms of attention demands suggested by Ladefoged and Broadbent. It is argued that this explanation was unnecessary, and that negative displacement can be expected in a system which analyses speech by discrete units.